The present invention relates generally to ready-to-stuff type food casings having sufficient moisture content that further moisture need not be added prior to stuffing. The invention especially relates to such casings which contain an antimycotic agent to prevent spoilage of the food casing prior to use.
Food casings, and more particularly, sausage casings like those made of regenerated cellulose and collagen have been widely used for years in processing frankfurters, sausages, bologna, salamis, etc. Tubular casings of regenerated cellulose, for example, are manufactured by extruding viscose into a fibrous web which is then regenerated in a coagulating bath. The regenerated gel casing is washed and plasticized usually in a glycerin containing bath. The plasticized gel film is inflated and passed through lengthy gas fueled hot-air dryers where the moisture content of the casing is reduced to a relatively low level, e.g. 5 to 10 percent. The dried casings may be shirred into tightly compressed strands and packaged. They may be stored for indefinite time periods or shipped to meat processing plants for stuffing at some later time. Before being used by meat processors the tubular strands or flat large size casings are customarily soaked in water to increase their moisture content usually to 30 to 55 percent on an "as is" basis (total casing weight). The extra moisture imparts additional plasticization and flexibility to withstand high speed stuffing without tearing and permits tutular shirred strands to extend smoothly without breaking.
The foregoing protocol, relating to plasticized and dried cellulosic casings, ordinarily does not present special problems with regard to preservation from molds, yeasts and bacteria developing during storage. This is true because such casings contain from 18-25 percent by weight glycerin and/or propylene glycol which in addition to being plasticizers incidentally impart microbicidal properties to the casing. In addition, by maintaining relatively low moisture levels during packaging and storage, conditions favoring germination of microbes are minimized.
However, with the advent of newer automated meat processing equipment, there has been greater emphasis on stuffing operations where pre-soaking procedures for casings at the meat packing plant are totally eliminated. Therefore, with greater frequency, casings are being supplied to food processors as ready-to-stuff shirred strands and flat reelstock, particularly where large size casings are used for salamis, bologna, meatloaves, cooked and smoked ham butts, etc. Because of the relatively high moisture levels of ready-to-stuff type casings, bacteria, yeasts and molds, can form on the casings during storage.
Where such casings are regenerated cellulose they have been manufactured as previously described, except after addition of a plasticizer such as glycerin, the casing is dried and then remoisturized.
It was not uncommon to find the practice of drying after addition of plasticizer, to allow other process steps. For instance, printing on casing sidewalls or for application of peeling aids or to reduce the moisture content to a level thought more conductive for shirring. As a final step however, much of the water previously removed by driers was then added back to the casings in order to place the casings in ready-to-stuff condition. Accordingly, previous ready-to-stuff type casings were mainly dependent on relatively high concentrations of costly chemical type plasticizers as primary plasticizers which incidentally also inhibited the development of microbes.
Such high concentrations of chemical type plasticizers however, may pose a potential indirect health hazard. Those casings containing such high levels of propylene glycol, glycerin and other similar type materials may in some instances diffuse from the casing sidewall into the surface of the encased meat product after stuffing. The level of antimycotic agent present although relatively high, would not prevent spoilage throughout the packaged meat product, but could mask visual evidence of meat spoilage and deterioration typically manifested by the appearance of sliming, souring or greening formation on the surface. Accordingly, such high levels of polyols added to food casings primarily as plasticizers may block the natural indicators of food spoilage which are necessary for consumer safety.
Premoisturized, ready-to-stuff type casings relying on high levels of chemical type preservatives and primary plasticizers are described in the following patents:
U.S. Pat. No. 1,868,203 discloses a process for preparing natural type sausage casings by treating in a 20 percent solution of glycerin and water. The casings can be immediately filled with meat or dried to remove moisture and stored for indefinite periods without deterioration. U.S. Pat. No. 2,802,744 discloses premoisturized, ready-to-stuff alginic acid or alginate sausage casings which may have water contents of 150 percent. 15 to 40 percent glycerin may be added onto the casing as a plasticizer. Such casings can be packaged in polyethylene bags and stored.
U.S. Pat. No. 3,617,312 discloses a polymeric water insoluble overcoating for dry sausage casings containing an antimycotic agent which slowly leaches from the overcoating after the casing is stuffed with meat emulsion. These casings were not premoisturized and packaged and required an additional water insoluble polymer such as a polyester or polyacrylic. Furthermore, the antimycotic agent was primarily in the overcoating rather than throughout the casing. The antimycotic agents incorporated into the water insoluble polymer could include, among many others, lower alkyl esters of p-hydroxybenzoic acid.
U.S. Pat. No. 3,864,499 discloses conventional dried casings treated with a high percentage of glycerin plasticizer. The glycerin containing casings, which are soaked prior to stuffing, are treated with additional oil soluble antimycotic agents, e.g. alkyl esters of p-hydroxybenzoic acid, dispersed in a viscose composition containing colloidal sized droplets of oil and organic cosolvents. The colloidal sized oil droplets prevent removal of the additional antimycotic agent during soaking prior to stuffing.
U.S. Pat. 3,981,046 relates to the humidification of cellulosic food casings carried out by the application to the interior of such casings of an aqueous solution containing at least 25 percent chemical type plasticizer. The plasticizers include various polyols, such as glycerin, propylene glycol, PEG and the like, the amount of glycerin present being suitable to plasticize the casing. The plasticizers also operate to retard imbitition of water by the casing.
U.K. Patent Specification No. 1,593,996 describes premoisturized large size tubular food casings containing from 25 to 71 percent moisture based on total weight of dry cellulose in the casing, wherein the casings also contain from 25 to 40 percent glycerin based on dry weight of cellulose present and an even higher percent glycerin when based on weight of liquid in the casing. In addition to glycerin, other antimycotic agents are suggested to prevent mold and fungi growth. U.K. Patent Specification No. 1,584,435 discloses in a preferred embodiment a premoisturized food casing having at least 27 percent by weight moisture content based on dry cellulose. The casings require 25 to 40 percent glycerin and at least 15 percent propylene glycol based on dry weight of cellulose for storagability to inhibit development of microorganisms. Other antimycotic agents are also mentioned for use along with the polyols, such as alkali metal and alkaline earth metal salts of propionic acid or sorbic acid and lower alkyl esters of p-hydroxybenzoic acid including the methyl, ethyl or propyl esters, preferably in amounts of at least 2.5 percent by weight of liquid components in the casing. The tubular cellulosic food casings described therein may be prepared by applying the essential amounts of water and antimycotic agent to suitable "dried" tubular food casings. U.K. Application No. 2,071,988 also relates to preparation of premoisturized casings having up to 40 percent water based on total casing weight. In order to control the development of molds, etc., the water activity of the casing is controlled by means of various chloride salts, e.g. sodium chloride, magnesium chloride, ammonium chloride, etc., preferably when used in combination with another antimycotic agent, as for example, propylene glycol. Glycerol may also be added to the casing. U.S. Pat. No. 4,409,251, like that of U.K. Application No. 2,071,988 controls the development of mold, yeast and bacteria prior to stuffing by maintaining the water activity of the casing at a sufficiently low level in conjunction with a glycerin content in the casing of at least about 40 weight percent based on the total weight of dry cellulose in the casing and again even a greater percent glycerin when based on liquid in the casing.
German Patent Publication No. P 29 26 590 5 discloses high moisture casings which are sterilized by heat and stored in sterile packages. Such heating is energy intensive and is therefore undesirable. In addition the heating of such casings to sterilization temperatures can adversely affect the properties of the casing. The preserved, premoisturized casings disclosed above require high temperature sterilization or else require relatively high levels of polyols as plasticizer, and therefore, requirements for water as the primary plasticizer are reduced. Besides relying on glycerin, propylene glycol and other costly polyols for microbicidal and plasticizing properties, ready-to-stuff casings in many of the above instances are dried in energy intensive dryers or else require high temperature sterilization. Accordingly, there is a need for an improved ambient temperature preserved, premoisturized ready-to-stuff type sausage casing which can be stored indefinitely without developing molds, yeasts or bacteria wherein water performs as the sole or principal plasticizer.